1. Field of the Invention
The present invention relates generally to a handoff system and method between a wireless Local Area Network (LAN) and a mobile communication network. In particular, the present invention relates to a system and method for providing a continuous service while an access terminal capable of accessing both a mobile communication network and a wireless LAN performs a handoff between the wireless LAN and the mobile communication network.
2. Description of the Related Art
In general, when a dual-mode access terminal (AT) capable of accessing both a cellular mobile communication network and a wireless local area network (LAN) is allocated an Internet Protocol (IP) address after accessing the wireless LAN and thereafter performs a vertical handoff to the mobile communication network, the AT uses a new IP address allocated from the mobile communication network instead of the existing IP used in the wireless LAN. For example, a Code Division Multiple Access 2000 (CDMA2000) mobile communication system allocates an IP address to an AT using an Internet Protocol Control Protocol (IPCP). The IPCP allocation method and system will now be described with reference to the accompanying drawing.
FIG. 1 is a diagram illustrating a conventional IP packet delivery process where an AT moves from a wireless LAN to a mobile communication network.
In a wireless LAN 40, an IP packet is delivered from an Internet network 30 to an AT 10 via an access router (AR) 42 and an access point (AP) 41 along a bold line 101. The AR 42 performs IP routing and vertical handoff on the AT 10 that accesses the Internet network 30 via the wireless LAN 40. The AR 42, when it supports Mobile IP, can serve as a foreign agent (FA). The AP 41 performs a wireless LAN access protocol with the AT and serves as a bridge between a wireless LAN and a wire network.
When the AT 10 moves from the wireless LAN 40 to a cellular network 20 which is a mobile communication network, an IP address of the AT 10 is updated through a process of FIG. 2, and an IP packet is delivered from a correspondent node (CN) 50 to the AT 10 via the Internet network 30, a packet data service node (PDSN) 22 and a base station system (BSS) 21 along a bold line 102.
A description will now be made of an IP allocation method in the mobile communication network for the foregoing system.
FIG. 2 is a signaling diagram illustrating a conventional IP allocation method in a mobile communication network.
Referring to FIG. 2, an AT 10 performs traffic channel (TCH) setup to a BSS (or 1×BSS) 21 in step 201. Then the BSS 21 performs remote node-PDSN session (R-P session) setup to a PDSN 22 in step 202. The PDSN 22 performs Point-to-Point Protocol (PPP) connection and accounting/authentication on a subscriber that accesses the Internet network 30 via the mobile communication network, and provides a vertical handoff service to the subscriber. Also, the PDSN 22, when it supports Mobile IP, can serve as a foreign agent (FA).
Thereafter, the AT 10 performs Link Control Protocol (LCP) negotiation with the PDSN 22 in step 203, performs Challenge Handshake Authentication (CHAP) authentication with the PDSN 22 in step 204, and performs IPCP negotiation with the PDSN 22 in step 205, thereby allocating an IP address. A format and type of an IPCP message will now be described with reference to Table 1 and Table 2.
A header of the IPCP message, as shown in Table 1, includes an 8-bit Code(1) field, an 8-bit Identifier(1) field, a 16-bit Length(2) field, and a variable-length Data(Variable) field.
TABLE 1123456789012345678901234567 8 9 0 1 2Code(1)Identifier(1)Length(2)Data(Variable)
TABLE 2CodeDescription0Vendor Specific1Configure-Request2Configure-Ack3Configure-Nak4Configure-Reject5Terminate-Request6Terminate-Ack7Code-Reject
The types of IPCP messages are classified as shown in Table 2 based on the bit value of each code.
In the conventional IP allocation method, the system can neither maintain sessions of upper layers (TCP/UDP layer and application layer) nor receive a packet being delivered to an AT during a vertical handoff process.
The network configuration of FIG. 1 can use Mobile IP to maintain upper layer sessions and provide seamless handoff during a vertical handoff process of the AT 10.
FIG. 3 is a diagram illustrating an IP packet delivery operation where an AT moves from a Mobile IP-based wireless LAN to a mobile communication network.
Referring to FIG. 3, when an AT 10 moves from a wireless LAN 40 to a cellular network 20 which is the mobile communication network, an IP packet is delivered from a CN 50 to the AT 10 via a Mobile IP-based home agent (HA) 60 through an existing IP tunneling route 301 and a new IP tunneling route 302 connected to the mobile communication network.
In the case where Mobile IP is used, the AT 10 can maintain the same IP address even after the vertical handoff, using a home address managed through the HA 60. The HA 60 intercepts a packet being delivered to the AT 10 via the existing IP packet delivery route 301, and delivers (forwards) the intercepted packet to the AT 10 through the new IP tunneling route 302, thereby providing a substantially seamless handoff service. However, in Mobile IP, a time delay may occur due to mobility determination and signaling transmission, and traffic is concentrated in the HA 60 because the HA 60 must intercept the packets being delivered from the CN 50 to the AT 10.